1. Field of the Invention
The present invention relates to a full-circumferential flow pump having a pump casing made of sheet metal, and more particularly to a full-circumferential flow pump having a pump casing which is made of sheet metal such as stainless steel plate and formed by press working.
It has been customary to press sheet steel such as stainless steel into a pump casing according to a deep drawing process. The pump casing has a casing flange, at the open end thereof, which extends radially outwardly and is formed integrally by press working. The casing flange has a plurality of bolt holes and is fixed to a holding member such as a bracket using bolts passing through the bolt holes, thereby holding the pump casing. The pressed casing flange must meet mechanical strength requirements for bearing an internal pressure developed in the pump casing, and also rigidity requirements for keeping a sealing surface stable. In conventional pressed pump casings, the casing flange has the same thickness as the pump casing body.
Inasmuch as the pressed pump casing is of a relatively flexible structure, however, it is impossible for the casing flange itself to satisfy both the mechanical strength requirements and the rigidity requirements. To achieve a desired level of rigidity of the casing flange, the conventional pressed pump casings have employed a steel sheet whose thickness is greater than the thickness required to withstand an internal pressure developed therein, or a cylindrical reinforcing portion folded from the outer circumferential edge of the casing flange and extending axially for reinforcing the casing flange, or a reinforcing member having a complex shape and made of the same material as the pump casing body.
As described above, the rigidity of the casing flange has been increased by employing either a steel sheet whose thickness is greater than the thickness required to withstand an internal pressure developed in the pump casing, or a reinforcing portion at the outer circumferential edge of the casing flange. The steel sheet of increased thickness is however difficult to press to shape.
On the other hand, in case of providing a reinforcing member of complex shape results in an increase in the cost of manufacture of the pump casing.